This invention relates to optical devices, and more particularly to optical transmitters and/or optical receivers.
Optical transponders include a combination of at least one optical transmitter and at least one optical receiver thereby providing input/output functions in one device. The use of optical networks is increasing. The bandwidth of the signals that optical transmitters can transmit, and the bandwidth of the signals that optical receivers can receive, is progressively increasing.
It is often important that optical devices such as optical transmitters and optical receivers be miniaturized. Miniaturization of optical devices is challenging. For example, positioning components close together may cause electromagnetic interference (EMI) of one optical device (or component thereof) to interfere with another optical device (or component thereof). Additionally, the amount of heat that is generated (and thus has to be dissipated) is similar regardless of the size of the component. As such, miniaturized optical devices have to dissipate more heat for a given volume. As such, many designs employ thermoelectric coolers to control thermal exposure of critical optical elements such as lasers. Alternatively, they may have distinct heat generating devices (such as lasers and laser drivers within optical transmitters) separated by a considerable distance or in separate packages. However the laser driver supplies a radio-frequency electrical signal to the laser, and as such is located relatively close thereto. Spacing the components within an optical device may also result in electrical conductors that extend between certain ones of the components. An extended electrical conductor can act as a transmitting or receiving antenna of EMI or a parasitic element degrading high frequency performance.
Optical transmitters and optical receivers typically include both optical and electronic (microwave) portions. In optical transmitters, an electrical signal received and processed by the electronic portion is converted into an optical signal and then transmitted over an optical fiber cable. In optical receivers, an optical signal received over an optical fiber cable is processed by the microwave portion and then transmitted as an electrical signal.
A design challenge involves repairing, replacing, or updating any optical device that is mounted to a circuit board. It would be desired to effectively replace one optical device (having both electronic and mechanical connections) by another optical device. Removal of an optical device involves not only mechanical connections, but electrical connections between the optical device and the circuit board must also be disconnected. To insert a replacement optical device, the applicable optical device similarly is secured by providing a mechanical connection as well as an electrical connection to the circuit board.
Materials play an important role in the design of optical devices. The device packages that enclose optical transmitters or optical receivers must adapt to a variety of mechanical, thermal, electrical, and optical conditions. For instance, the different portions of the device package are configured to withstand thermomechanical stresses, vibrations, and strains that are applied by, e.g., outside forces to the device package which houses the optical device. It is also required that different parts of the optical device can tolerate different thermal expansions that would otherwise create excessive stresses or strains in the device package resulting in optical instability. Thermal conditions also relate to the capability of operating successfully at a series of high or low temperatures, depending on the application. Additionally, the optical device has to provide the optical and electrical functions for which it is designed. As such, the materials selected play an important role in allowing the optical device to perform its desired function.
In one aspect, it would be desired to provide an optical device that is designed to operate under the variety of thermal, mechanical, optical, and/or electrical conditions that the optical device will potentially encounter over its life. In another aspect, it would be desired to provide a Faraday cage to limit the transmission of electromagnetic interference through a part of a device package case of an optical transmitter or optical receiver. In yet another aspect, it would be desired to provide effective heat sinking from one or more heat generating components within an optical component. In yet another aspect, it would be desired to provide an effective surface mount to secure an optical transmitter or optical receiver to a circuit board.
The present invention is directed to a variety of aspects of an optical transponder that includes an optical transmitter, optical receiver or similar devices. One aspect includes Faraday cages in an optical transmitter or optical receiver. Another aspect includes effective configurations of heat sinks that limit heat transfer between a plurality of heat generating sources in an optical transmitter or receiver. Another aspect involves providing surface mounts that secure the optical transmitter and/or optical receiver to a circuit board or heat sink. Another aspect involves providing one or more passive electronic components on a header or transmitter optical bench that supports an optical source such as a laser.
One aspect includes an optical transmitter, an optical receiver, a circuit board, a first thermally conductive and electrically insulative adhesive pad, and a second electrically and thermally conductive adhesive pad. The circuit board includes a first mounting region and a second mounting region. The first mounting region is configured for mounting the optical transmitter and the second mounting region is configured for mounting the optical receiver. The first adhesive pad includes two substantially planar faces. Each one of the planar faces of the first adhesive pad is coated with an adhesive that facilitates a first affixing of the optical transmitter to the first mounting region whereby the optical transmitter remains affixed through a range of operating temperature and pressures. The first adhesive pad has a first prescribed thickness. The optical transmitter is configured to allow electrical and optical mounting when the first adhesive pad secures the optical transmitter to the circuit board. The second adhesive pad includes two substantially planar faces. Each one of the planar faces of the second adhesive pad is coated with an adhesive that facilitates a second affixing of the optical receiver to the second mounting region whereby the optical receiver remains affixed through a range of operating temperature and pressures. The second adhesive pad has a second prescribed thickness. The optical receiver is configured to allow electrical and optical mounting when the second adhesive pad secures the optical receiver to the circuit board.
Another aspect relates to a ceramic wall portion which, in one embodiment is configured as a ceramic confinement cavity. The ceramic wall portion is constructed with a metal configuration that limits the passage of EMI through the ceramic wall portion. The ceramic wall portion includes a plurality of laminated ceramics layers and a plurality of vias. Each one of the laminated ceramics layers extends substantially parallel. The plurality of vias extend substantially perpendicular to the plurality of laminated ceramic layers and through the laminated ceramic layers. The plurality of vias are configured to form a pattern that limits the passage of EMI through the vias. In one embodiment, the ceramic wall portion partially defines a Faraday cage that surrounds an optical device.
Yet another aspect relates to a method of manufacturing a ceramic wall portion that is configured to act as a portion of a Faraday cage. The method includes providing a ceramic layer and depositing a metalization pattern on an upper surface of the ceramic layer, wherein the metalization pattern forms an electric pattern to which an electric lead interconnect may be attached. The method further comprising cofiring the ceramic layer with the deposited metalization pattern.
In accordance with another aspect, a Faraday cage is configured to enclose the optical device. The Faraday cage extends between a baseplate and a lid. The lid is vertically spaced from the baseplate. The Faraday cage limits the passage of EMI. The Faraday cage includes one or more ceramic wall portions and a plurality of vias. The ceramic wall portions extend from the baseplate to the lid and limit the passage of EMI through the ceramic wall portions. The ceramic wall portions include a plurality of laminated ceramic layers. The plurality of vias extend substantially perpendicular to the baseplate through the laminated ceramic layers. Each one of the plurality of vias extends substantially from the baseplate to the lid. The vias are configured to form a pattern that limits the passage of EMI through the vias. In one embodiment, the baseplate, lid, and one or more ceramic wall portions define a Faraday cage that surrounds an optical device.
Another aspect relates to a receiver optical bench comprising a substrate, a fiber receiving area, a lens mounting area, and a reflective area. The fiber receiving area, the lens mounting area, and the reflective area are positioned linearly. The fiber receiving area includes a V-groove. The V-groove geometry is etched or otherwise micromachined (e.g., laser ablation, e-beam techniques, high pressure waterjet cutting, microgrinding and the like) in the substrate. A length of optical fiber cable is inserted in said V-groove to facilitate alignment of the length of optical fiber cable towards the lens mounting area. The lens mounting area includes first support members for supporting a lens. The lens is positioned to facilitate directing of light from said optical fiber cable towards said reflective area. The reflective area includes a planar mirror and second support members. The second support members support a photodiode positioned above the planar mirror. The planar mirror is positioned at a slanted angled to facilitate directing of light from the lens to the photodiode. In one embodiment, the receiver optical bench is assembled using only passive alignment techniques that do not require biasing of the photodiode to properly align the fiber in the bench.
In accordance with yet another aspect, a heat generating component is mounted on a header or transmitter optical bench to enhance heat sinking characteristics. A pedestal physically supports, and is configured to dissipate heat present on, the header or transmitter optical bench. The pedestal is laterally defined by any lateral surface of the header or transmitter optical bench and bounded on at least one side by a vertical surface of an air trench. The heat generating component is positioned only in areas on the header that have an associated heat dissipation conical region extending from the heat generating component downward through the pedestal at an angle from the vertical of approximately 45 degrees (35-55 degrees) that satisfies Fourier""s Law of Heat Conduction, wherein the conical region does not intersect the vertical surface of the air trench. A second pedestal may be positioned on the side of the air trench opposite the first pedestal. The second pedestal may, for example, support a hybrid subassembly having a laser driver mounted thereon.
In yet another aspect, a header assembly is provided for use in an optical transmitter. The header assembly includes a header or transmitter optical bench, a laser, and at least one passive electronic component. The laser is mounted on the header or transmitter optical bench. At least one passive electronic component is mounted on the header or transmitter optical bench. The at least one passive electronic component is one from the group of an inductor, a capacitor, and/or a resistor. In one embodiment, the header or transmitter optical bench is on the order of 5 mm in width or less.
Yet another aspect relates to an optical transmitter comprising a header or optical bench, a hybrid subassembly, a laser mounted on the header or transmitter optical bench, and a laser driver mounted on the hybrid subassembly. An air trench is formed between the header or transmitter optical bench and the hybrid subassembly.
Still another aspect relates to a method of positioning a heat generating component on a header or optical bench to enhance the heat sinking characteristics of the header or transmitter optical bench. The method includes positioning the header or optical bench on a pedestal that is laterally defined by any lateral surface of the header or transmitter optical bench and any vertical surface defining an air trench. The method includes defining those areas on an upper surface of the pedestal that violate Fourier""s Law of Heat Conduction based on extending from any heat generation device downward at an angle of approximately 45 degrees (i.e., 35-55 degrees) to form a conical region. The conical region does not intersect with any one of the lateral surfaces of the header or any one of the vertical surfaces defining the air trench. The method further includes positioning the heat generating component at only those locations on the upper surface of the pedestal that do not violate Fourier""s Law of Heat Conduction.
Yet another aspect relates to an optical transmitter that includes a planarized header or optical bench, a laser mounted on the planarized header or transmitter optical bench, and a temperature sensor located on the planarized header or transmitter optical bench. The axis of light emitted from the laser is parallel to the plane of the header or optical bench. The temperature of the laser is obtained from the output of the temperature sensor without application of an offset to the temperature sensor output. In one embodiment, the header or transmitter optical bench is 5 mm or less in width, and the temperature sensor is positioned within 2.5 mm of the laser. In a further embodiment, the temperature sensor is positioned within 1 mm of the laser.
Still another aspect relates to an apparatus for mounting an optical device including an adhesive pad including two substantially planar faces. Each one of the planar faces is coated with an adhesive facilitating mounting said optical device to a circuit board or pedestal so the optical device remains affixed through a range of operating temperature and pressures. The adhesive pad has a prescribed thickness for facilitating said affixing.
Still another aspect relates to a method of removing an optical device from a circuit board, wherein the device package is secured to the circuit board using an adhesive pad. The method comprising peeling a portion of the adhesive pad away from the circuit board. An optical device removal tool is then inserted between the optical device and the circuit board. The optical removal tool has a pair of fork portions and a cavity positioned between the fork portions. The fork portions straddle one or more leads on the optical device. Following insertion, the remainder of the adhesive pad is pryed away from the circuit board using the optical device removal tool. In one embodiment, the cavity between the fork portions of the removal tool extends into the handle of the removal tool.
Yet another aspect of the present invention is directed to a reconfigurable laser header assembly that can be used to properly bias either an n-doped laser substrate structure or a p-doped laser substrate structure. The reconfigurable laser header assembly includes a header that is coupled to a modulated electric (AC) current source, a (DC positive) bias electric current source, and a DC negative electric current source. The header assembly also includes a laser mounted on the header, and an electrical conductor formed from first and second metalized regions. The laser includes a base electric contact and a laser electric contact. Each of the first and second metalized regions is in electrical connection with the base contact. Different ones of the modulated electric (AC) current source, the (DC positive) bias electric current source, and the DC negative electric current source can be electrically connected to the first and second metalized regions, and the laser electric contact in a manner to properly bias the laser regardless of whether the laser is an n-doped laser substrate structure or a p-doped laser substrate structure.
Yet another aspect relates to an optical isolator that includes a first magnetic polar source, a second magnetic polar source, and an optical element. The first magnetic polar source has a first magnet axis. The second magnetic polar source has a second magnet axis, wherein the first magnet axis is maintained substantially parallel to the second magnet axis. The optical element is positioned between the first and second magnetic polar sources, and has a length measured along the first magnet axis that is less than the length of the first magnetic polar source along the first magnet axis. The optical element has a central axis that is tilted by an angle of from 2 to 12 degree from the first magnet axis. The optical isolator is aligned and positioned in the transmitter package case using magnetic attraction between the package case and the magnetic polar sources.
In preferred embodiments, the optical transmitter of the present invention includes a laser that operates in the range of 1260-1360 nm. The laser is in a transmitter package case that covers less than 0.30 square inches of surface area on a board to which the package case is mounted. Alternatively, the transmitter package case is less than 0.062 cubic inches in volume. The transmitter package case is positioned within a housing case. The optical transmitter continues to function in compliance with the transmission requirements of International Telecommunciations Union (ITU-T) Standard G.693 and/or G.691, the Synchronous Optical Network Transport System (SONET/SDH) Standard STM-64 and/or the SONET Standard OC-192, without thermoelectric cooling, when the thermal resistance of the transmitter package is less than or equal to 0.7 degrees C. per Watt and an external temperature of the functioning transmitter package case is at or within 1xc2x0 C. of a temperature of the laser, and/or when the thermal resistance of the housing case is less than or equal to 1.1 degrees C. per Watt and the external temperature of the functioning housing case is at or within 5xc2x0 C. of a temperature of the laser.